Epoxy resin compounds are used in a wide variety of applications including in coating formulations or compositions for coating applications. While some epoxy resins such as epoxy novolac resins show good chemical resistance properties, such epoxy resins are very viscous and cured coatings prepared from these epoxy resins are very brittle with low impact resistance and poor damage tolerance.
Typically, epoxy resins that are very viscous or contain high solids will necessitate the use of solvents to reduce the initial viscosity of the formulated epoxy resin, for example to below 2000 mPa-s at 25° C. An epoxy resin with a lower viscosity facilitates handling a curable composition containing such low viscosity epoxy resin and facilitates applying the composition as a coating to a substrate. However, the solvents, used to reduce the viscosity of the epoxy resins, are usually a source of undesirable volatile organic compounds (VOCs) when using a solvent-borne composition. Therefore, heretofore attempts have been made to avoid using a solvent in a curable epoxy resin composition.
For example, EP590975 (A1) discloses a low viscosity substantially solvent-free one-component type epoxy resin adhesive composition including (a) 100 parts of a conventional epoxy resin such as a bisphenol A or a bisphenol F type epoxy resin; (b) 5-100 parts of a reactive diluent such as cresol glycidyl ether or cyclohexanedimethanol diglycidyl ether with a viscosity of less than 1,000 mPa-s at room temperature (about 25° C.); and (c) 1-100 parts of a microencapsulated amine latent curing agent. Thus, the solids content of the composition disclosed in EP590975 (A1) is essentially 100%. EP590975 (A1) also describes blending a conventional epoxy resin with cyclohexanedimethanol epoxy resin (at a concentration of approximately 5 wt % to 50 wt %) to reduce viscosity. However, the composition of EP590975 (A1) is used as an adhesive, not as a coating. In addition, the composition disclosed in EP590975 (A1) does not have the low chloride levels or purity levels required for meeting the performance properties of the resulting coating made from such a composition.
The use of reactive diluents in coating compositions also has some disadvantages. For example, reactive diluents can reduce the performance properties (for example, chemical resistance, impact resistance, water resistance, and corrosion resistance) of the resulting coating made from such a composition containing reactive diluents.
U.S. Pat. No. 8,318,834 discloses an epoxy resin reactive diluent composition including (A) an epoxy resin diluent such as a cis, trans- 1, 3- and 1, 4-cyclohexanedimethylether moiety; and (B) a resin compound including one or more epoxy resins other than the epoxy resin diluent (A). The above epoxy resin reactive diluent composition is combined with a curing agent and/or a curing catalyst therefore to form a curable epoxy resin composition. The curable epoxy resin composition can then be cured to form a cured epoxy resin. U.S. Pat. No. 8,318,834 does not disclose 1,4-CHDM epoxy resin, an isomer of UNOXOL epoxy resin.
Others heretofore have used blends of epoxy resins in an attempt to form a curable epoxy resin composition useful for applications other than coatings and without the disadvantages above. For example, JP08012741 and JP10226745 disclose blending a conventional epoxy resin with cyclohexane dimethanol diglycidyl ether as a diluent (33 wt % to 60 wt %) to reduce viscosity and formulate a low viscosity liquid epoxy blend composition used as an impregnant for electronic parts applications. The composition of JP08012741 and JP10226745 contains 100 parts of bisphenol A epoxy resin; 50 parts to 150 parts of cyclohexane dimethanol diglycidyl ether, a ratio of equivalents of acid anhydride type curing agent to epoxy groups of from 0.8:1 to 1.1:1; and 0.1 part to 5 parts of a curing promoter. JP08012741 and JP10226745 do not disclose the use of an epoxy resin composition for a coating application.
With regard to viscosity, JP08012741 describes a low viscosity epoxy composition having a viscosity of less than 300 mPa-s as measured with a B-type viscometer at 25° C. And, JP10226745 describes a formulated low viscosity epoxy composition with a viscosity of less than 200 mPa-s at 25° C. as measured with an E-type viscometer. JP10226745 further discloses a pot-life of the composition which is defined as the time it takes the viscosity of the formulated composition to reach 1,000 mPa-s after keeping the composition at 40° C., and wherein the viscosity is measured at 25° C. with an E-type viscometer.
In addition, curing of the composition disclosed in JP08012741 and JP10226745 is carried out with an anhydride curing agent and not with an amine curing agent. Curing of the composition disclosed in JP08012741 and JP10226745 is forced at an elevated temperature. For example, the curing temperature of the composition disclosed in JP08012741 is 100° C. to 130° C. (by immersing a preheated film condenser to 100° C. to 130° C. into 20° C. to 50° C. liquid epoxy compositions). The composition of JP08012741 includes a combination of an epoxy resin, cyclohexane dimethanol diglycidyl ether, anhydride curing agent, and an imidazole catalyst.
The curing temperature of the composition disclosed in JP10226745 includes heating the composition at a temperature of 80° C. for 2 hours followed by further curing the composition at a temperature of 120° C. for 2 hours. The composition of JP10226745 includes a liquid cyclo-epoxy resins (A) (at 10° C. to 35° C. the epoxy resin is liquid); cyclohexane dimethanol diglycidyl ether (B) (<100 mPa-s at 25° C.); anhydride curing agents (C); catalyst solution, 50 wt % solid, (D); and with or without reactive epoxy diluents with viscosity less than 30 mPa-s at 25° C. Neither JP08012741 nor JP10226745 disclose a curing temperature being at ambient temperature (about 25° C.).
What is needed in the coating industry is a low viscosity, solvent-free epoxy resin composition containing a blend of epoxy resins that when formulated into a curable composition cures rapidly; and such that when cured, the resulting cured coating exhibits improved performance properties such as good resistance to moisture and corrosion. In addition, there is a need in the coating industry for easy to apply chemical resistant coatings with good flexibility and good impact resistance.